1. Field of the Invention
The present invention relates to a technique for searching a recommendable route to a destination and calculating an estimated travel time needed for the route in a navigation apparatus installed in a vehicle, etc.
2. Description of Related Art
With respect to a navigation apparatus installed in a vehicle, there has been known a technique of searching a route extending from a departure place to a destination on the basis of road map data and suggesting the route thus searched as a recommendable route to a user.
Such a recommendable route searching operation is carried out by searching (selecting) a route needing the minimum cost in available routes between the departure place and the destination according to a technique called as xe2x80x9cDijkstra algorithmxe2x80x9d or the like. In this method, the total distance of the route or the travel time needed for the route is usually selected as the xe2x80x9ccostxe2x80x9d defined in this method.
The estimated travel time needed for the route (hereinafter merely referred to as xe2x80x9cestimated travel timexe2x80x9d) is calculated as follows. When a recommendable route is determined, the length of each of the roads constituting the recommendable route is weighted with the value corresponding to the type of each road (expressway, public road or the like) to set the value thus weighted as a travel time for each road, and the estimated travel time is calculated on the travel times for the roads.
Recently, there has been put into practice a traffic information communicating system for supplying traffic information to users of vehicles through communications, which is known as VICS (the trademark of the foundation of Traffic Information Communication System Center).
According to this traffic information communication system, traffic information such as traffic jams, traffic regulations, etc. is transmitted from the center to vehicles by optical beacons or electric wave beacons disposed on roads or by FM multi-broadcasting, thereby enabling real-time use of traffic information in the vehicles. In a conventional navigation apparatus, when traffic regulation information is received from such a traffic information communication system, the contents representing the traffic regulation information are notified to users in the form of characters, voices and displays of figures on a road map.
The above-described conventional technique for calculating an estimated travel time needed for a recommendable route has the following problem.
That is, the travel time needed for the recommendable route is calculated on the basis of fixed parameters such as the length of each road, the type of each road, etc., and thus when some roads of the recommendable route suffer from traffic jam for traffic regulation such as one-way traffic or the like, the estimated travel time thus calculated differs greatly from actual travel time.
Therefore, an object of the present invention is to calculate an estimated travel time for a recommendable route, which more meets an actual traffic condition.
In order to attain the above object, a route searching apparatus for searching a recommendable route to a destination includes: means for storing map data representing road maps; means for receiving traffic jam information representing traffic jam places and a travel time needed to pass through a section in which each of the traffic jam places is located by communication; and travel time calculating means for setting the travel time represented by the traffic jam information as an effective travel time for the traffic jam section represented by the traffic jam information thus received while setting a travel time calculated on the basis of the map data as an effective travel time for the other sections, calculating the sum of effective travel times for respective sections located between the current position on the searched recommendable road and a destination or a point on the recommendable route for which an estimated travel time is calculated, and displaying the sum of the effective travel times thus calculated as the travel time needed to travel from the current position to the destination or the point on the recommendable road for which the estimated travel time is calculated.
According to the above route searching apparatus, traffic jam information is picked up from a traffic information communication system such as VICS or the like and the estimated travel time is calculated in consideration of the traffic jam information. Therefore, even when a traffic jam occurs or traffic regulation is carried out, an estimated travel time conforming to the actual traffic conditions can be calculated.